1. Field of the Invention
This invention relates to cooling systems for electrical devices. More particularly, it relates to cooling systems for rack-mounted, electronic equipment.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Electronic equipment housed in a chassis is often mounted in a rack enclosure. A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic modules. Each module has a front panel that is 19 inches (480 mm) wide, including edges or ears that protrude on each side which allow the module to be fastened to the rack frame with machine screws, bolts or specialized fasteners.
Equipment designed to be placed in a rack is typically described as “rack-mount,” a “rack mounted system,” a “rack mount chassis,” “subrack,” “rack mountable” or, occasionally, simply “shelf.” The height of the electronic modules is also standardized as multiples of 1.75 inches (44.45 mm)—one rack unit or “U”. Most racks are offered in the 42U form—a single rack capable of holding forty-two 1U devices, or any combination of 1U, 2U, 3U or other rack unit heights that add up to 42 or less.
Because of their origin as mounting systems for railroad signaling relays, they are still sometimes called “relay racks,” but the 19-inch rack format has remained a constant while the technology that is mounted within it has changed to completely different fields. The 19-inch standard rack arrangement is widely used throughout the telecommunication, computing, audio, entertainment and other industries, although the Western Electric 23-inch standard, with holes on 1-inch centers, prevails in telecommunications.
Racks (and rack enclosures) are widely used for computer server and network switching equipment, allowing for dense hardware configurations without occupying excessive floor space or requiring shelving. Another use for rack-mounted equipment is industrial power, control, and automation hardware, typically in 46U racks. Racks and rack enclosures are typically constructed of steel or aluminum. Certain rack-mount cases are now also constructed of thermo-stamped composites including those comprising carbon fiber and/or aramid fiber (e.g., DuPont Kevlar) for demanding military and commercial uses.
Racks are available with either four or two vertical rails or “posts.” Four-post racks provide for mounting slides to support the equipment at both the front and rear. Four-post racks can also be provided with sides and front and rear doors. Two-post racks provide just two vertical rails. Equipment can be either mounted via the front panel holes or close to the center of gravity to minimize load on the front panel. Two-post racks are most often used for telecommunication installations.
Standards for a 19-inch rack are published by the Electronic Industries Alliance (EIA-310-D), Consumer Electronics Association (CEA-310-E) and the International Electrotechnical Commission
Rack-mountable equipment may be mounted simply by bolting its front panel to the rack, or, in the case of a square-holed rack, by clipping or other fastening means. Having all the structural support at one edge of the equipment can be a weakness of this system, and heavier equipment may be designed to use a second pair of mounting strips located at the back of the equipment. The strength required of the mounting strips means they are typically not merely flat strips but a wider folded strip arranged around the corner of the rack. The strips are usually made of steel having a thickness of about 2 mm (one standard recommends a minimum of 1.9 mm), or of slightly thicker aluminum.
Heavy equipment or equipment which is commonly accessed for servicing, for which attaching or detaching at all four corners simultaneously would pose a problem, is often not mounted directly onto the rack but instead is mounted via rails (or slides). A pair of rails is mounted directly onto the rack, and the equipment then slides into the rack along the rails, which support it. When in place, the equipment may also then be bolted to the rack. The rails may also be able to fully support the equipment in a position where it has been slid clear of the rack; this is useful for inspection or maintenance of equipment which will then be slid back into the rack.
Rack mount enclosures typically have solid side panels and either open or mesh front and back surfaces. The mesh may be in the form of a door that opens to permit access to the equipment mounted in the rack. The mesh may be an expanded metal mesh which is bonded to the rack and/or grounded to reduce electromagnetic interference (EMI). As part of this enclosure design, cooling air is directed to flow in or out of the front and rear of the enclosure. Perhaps the most common design is configured to draw cooling air in from the front of the enclosure and exhaust heated air from the back. It should be appreciated, however, that the terms “front” and “back” are somewhat arbitrary in this context since rack mounted equipment typically can be installed with either face towards the “front” of the rack mount enclosure.
Unused vertical space in open frame rack and rack enclosures can create an unrestricted recycling of hot air that may cause equipment to overheat and malfunction. This mainly occurs when hot exhaust air returns above or below the equipment and back to the air intake (“exhaust air recirculation”). Blanking panels can be used to reduce this problem. Blanking panels fill empty vertical spaces in the rack to maintain the desired front-to-back airflow. Plastic blanking panels that snap in to any square-holed rack enclosure and that can be installed without tools are available.
Equipment rooms having a large number of rack mount enclosures—e.g., data centers, server farms, and the like—are often configured with alternating “hot” and “cold” aisles between rows of rack mount enclosures. The enclosures are positioned such that their fronts face a “cold aisle” and their rear surfaces face a “hot aisle.” This enables the air handling equipment in the room to be designed such that cooled air is supplied to the cold aisles and warmed air is exhausted from the hot aisles. In some equipment rooms, the rack mount enclosures are supported on a modular, elevated floor which permits cables to be conveniently run to the enclosures. Relatively cool air can also be supplied to the cold aisles from grills located in the floor system. The entire elevated floor system may serve as a plenum for the cooler air.
It will be appreciated that, in such a system, the predominate airflow through the rack mount enclosures needs to be from front to back in order to achieve the best cooling performance. However, some rack-mounted equipment exhausts all or a portion of the cooling air through the sides of the chassis. This is particularly true of equipment having a large number of connections (ports) on the front or rear panel of the chassis. The side-exhausting equipment presents problems when the intended installation location is a conventional rack with front and rear airflow, particularly if a hot aisle/cold aisle arrangement is being used. The present invention solves this problem.